Ammoniated silica-alumina gel and catalyst containing the same and processes for producing same

Abstract

This invention relates to hydrothermal treatment of silica-alumina cogels resulting in a reduction in the NH.sub.4 content of the gel and the generation of a beta crystal phase and the employent of such gels as cracking catalysts.

Description

Prior to the introduction of the exchanged crystalline zeolites of the faujasite type, as a catalyst for cracking of hydrocarbons, a commonly used catalyst was composed of a silica-alumina cogel containing from about 3 to about 25 percent by weight of Al.sub.2 O.sub.3 on a volatile free basis.

Because of the substantially higher activity of the catalyst formed from crystalline zeolite, they have replaced to a large measure the silica-aluminum cogels as the primary component of a hydrocarbon conversion catalyst.

The literature relating to a silica-alumina gels and their catalytic properties is extensive (see Iler, "The Colloid Chemistry of Silica and Silicates", Chapter VI, Cornell Press [1955] Ed.) and citations there given. Milliken, et al., "Discussions Faraday Society" No. 8, "Heterogeneous Catalysis" p. 279, etc. (1950) Mills, et al., Journal of the American Chemical Society, vol. 72, pp. 1554-1556 (1950). See also: Erickson, U.S. Pat. No. 2,872,410; Winyall, U.S. Pat. No. 2,886,512; Wilson, U.S. Pat. No. 3,124,541; Magee, et al., U.S. Pat. No. 3,433,748; Haden U.S. Pat. No. 3,065,054; Maher, et al, U.S. Pat. No. 3,423,332; Lussier, et al, U.S. Pat. No. 3,974,099.

STATEMENT OF THE INVENTION

We have discovered that the catalytic cracking activity of the silica-alumina cogels which are substantially free of sodium or other alkali or other alkali metal cations may be materially improved by digesting the cogel at an elevated temperature in the presence of solutions containing hydrogen, ammonium or polyvalent cations such as rare earth or alkaline earth cations.

Gels so treated may, depending on the gel and the reaction system and the conditions of treatment, remain in the amorphous state or develop a crystalline phase.

Gels which have ammonium cations associated with the gel are herein referred to as ammoniated gels. Such gels for example may contain substantial concentrations of ammonium cations.

Gels may also be formed substantially free of ammonium cations by reacting sodium aluminate with an aluminum salt and maintaining the mixture on the acid side. The sodium content of the acid gel may be similar to that of the ammoniated gel. We refer to such gels as acid gels.

While hydrothermal treatment of the acid gel according to the process of our invention produces a gel of substantial catalytic activity, supeprior activity is obtained by treatment of the ammoniated gel.

In the case of the ammoniated gels the improvement in catalytic activity obtained by the hydrothermal treatment is increased by treatment at a temperature in excess of about 150.degree. F. In such ammoniated gels, preferably those containing SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of less than about 3, substantially free of sodium cations, the catalytic activity of the gel is increased to a degree which is dependent on the concentration of the ammonium cations associated with the treated gel. Preferably the NH.sub.4 content of the gel, expressed as NH.sub.3, is in the range from less than about 0.3 and preferably less than 0.2 equivalents of ammonium ion per mole of Al.sub.2 O.sub.3.

The activity produced from such gels depends on the conditions of the hydrothermal treatment and the ionic system. A crystalline phase may develop or the gel may remain amorphous and a reduction in the ammonium content of the gel and an increase in the catalytic activity of the gel may be obtained in both cases.

The activity may be measured by the microactivity cracking test described in the Oil and Gas Journal of Sept. 16, 1966; page 48, etc,; and Nov. 22, 1975; page 60, etc.

In the following examples the conditions in carrying out the above tests is as follows. The calcined pelleted catalyst was first steamed at temperatures and for times specified below and then used in cracking of a petroleum fraction under the following conditions. The oil charge is a wide boiling range high sulfur feed stock (boiling range about 430.degree. to 1000.degree. F.). The catalyst to oil ratio is 4. The weight hourly space velocity is 16.45 grams of oil per gram of catalyst per hour. The temperature of the reactor is 910.degree. F. The percent conversion is reported as the volume of liquid condensate product of boiling point range of up to 421.degree. F. based on the volume of liquid charge. The percent conversion when the catalyst is tested after calcination of the catalyst in air for two hours at 1450.degree. F. is termed M activity. When the calcined sample is steamed at 1500.degree. F. for two hours, prior to testing it is termed the S activity. When the calcined sample is first steamed for two hours at 1550.degree. F., prior to testing, it is termed S+ activity.

The process of our invention includes the treatment of a silica-alumina cogel containing less than about 1% of Na.sub.2 O based on the cogel on a volatile free basis by a hydrolytic treatment of the gel. The treatment may be carried out in the presence of monovalent cations other than alkali metal cations such as hydrogen or ammonium or polyvalent cations such as rare earth cations or alkaline metal cations. We prefer to carry out the hydrothermal treatment under acid conditions rather than at higher pH as for example under alkaline conditions. A superior amplification in the activity by reductions in ammonium content in the gel is obtained by treatment under acid conditions.

Under relatively mild and controlled hydrothermal conditions of temperatures below about 300.degree. F., the reaction of the gel having low Na.sub.2 O content, results in an amorphous gel which exhibits superior catalytic activity as compared with the original gel. At temperatures above about 350.degree. F. and at suitable concentrations of cations and time of digestion a crystalline phase develops.

The nature of the crystalline phase as evidenced by its x-ray spectrum depends on the nature of the cations employed in the hydrothermal treatment. The product of this application is produced by employing an acid solution of rare earth cations. The characteristic of the crystal phase developed in the gel depends on the conditions of the reaction for example, the ratio of the rare earth to the gel and the time of digestions at the above temperatures under autogenous superatmospheric pressure according to the invention of this application. A crystal phase is generated in the gel which acts as a host for the crystalline phase. For purposes of distinguishing the gel and the crystal phase from others which may be generated by variations in the hydrolytic treatment of the cogel, we have designated the crystal phase as "beta" and the gel which contains the "beta" phase as "beta" cogel.

The crystalline phase is characterized by an x-ray spectrum in which characteristic peaks occur. Excessive exposure of the gel for prolonged periods of time particularly at the higher temperatures may deliteriously affect the catalytic activity of the deammoniated gel although a successful reduction in ammonium content is achieved.

For purposes of describing the result of the process of treating the ammoniated gel with water or a solution of a salt, whereby the NH.sub.4 content of the gel is reduced, we refer to the process as an "exchange" and the cation as "associated" with the gel.

The cogel, which we prefer to treat by the process of our invention to form the catalyst of our invention may be produced by any of the methods used in the prior art to form such cogels in which the treatment results in a gel having an ammonium ion associated with gel as in the ammoniated gel referred to above.

The cogel, which may be hydrothermally treated according to our invention, may be formed by treating a mixture of silica hydrosol with aluminum salt in the ratios to produce a gel of the desired SiO.sub.2 /Al.sub.2 O.sub.3 ratio and exchanged with ammonium cation to reduce the sodium content of the gel.

We prefer to coprecipitate the silica-alumina hydrosol to form the gel from a mixture of sodium silicate and aluminum salt, e.g. aluminum sulfate, or aluminum nitrate or aluminum chloride made alkaline with ammonium hydroxide to reduce the sodium content as is more fully described below.

We have found that the improvement in the catalytic activity of a gel treated according to our invention depends on the silica to alumina ratio of the cogel. The ammonia content of the ammoniated gel of our invention depends on the silica to alumina ratio of the gel. The catalytic activity attainable by our invention is substantially greater as the molar weight ratio of SiO.sub.2 to Al.sub.2 O.sub.3 is less than about 3 and preferably about 1 to about 2.

Our preferred embodiment of our invention is to employ an ammoniated silica-ammonia cogel having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio in the range of about 1.25 to about 2.5, and an ammonium ion content of less than about 0.3 equivalents of ammonium cation per mole Al.sub.2 O.sub.3 to form a catalyst having a M activity in excess of 60%.

The preferred embodiment of the process for producing the "beta" cogel is to hydrothermally treat an ammoniated cogel with an acid solution of rare earth cations in amount of about 10% of the weight of the gel on a volatile free basis, at an elevated temperature to reduce the ammonia content of the gel to less than about 1% by weight of the treated gel to produce a beta crystal phase as set forth below.

We prefer to employ the gel formed when using the ammoniated cogel formed from aluminum sulfate.

EXAMPLE 1

5,017 grams of sodium silicate (28% SiO.sub.2 -8.9% Na.sub.2 O by weight) equivalent to 1,440 grams of SiO.sub.2 is dissolved in water. The slurry solution is acidified to a pH of 11 with sulfuric acid; 26,896 grams of an aluminum sulfate solution (equivalent to 1,560 grams of Al.sub.2 O.sub.3) is added gradually to the acidified slurry with constant agitation.

The pH at the end of the addition of the aluminum sulfate should be in the range of about 3 to about 3.5. The solution is passed through a colloid mill to be well homogenized. The homogenized solution is made alkaline with ammonium hydroxide with constant and vigorous agitation to adjust the mixture to a pH of about 8.5 to about 9.

The mixture is vigorously stirred and the pH is maintained in the range of about 8.5 to about 9 by suitable adjustment for about 1 hour to insure uniformity of the mixture. It is then heated to a temperature of about 75.degree. to 80.degree. C. for about 30 minutes and then immediately filtered and the filter cake washed with hot distilled water of about 80.degree. C. The wash filter cake is then slurried to a solid content of about 5% in distilled water which contained about 2% of ammonium nitrate and then filtered. The filter cake is then again slurried with ammonium nitrate solution as in the last previous step. The filter cake from the last step is again reslurried in an ammonium nitrate solution as above and filtered. The filter cake from the last filtration above is washed with distilled water.

The silica-alumina gel thus produced is preferably maintained in a sealed container prior to use in the catalyst of our invention. It should be used as promptly as possible since aging of the gel will impair its properties in producing a good attrition resistant catalyst.

The ammoniated cogel is amorhpous to K alpha copper radiation at 500 counts per second on the counter of the strip chart x-ray spectrum so produced. The gel produced as above, was employed in the following examples, except in Example 19 where the acid gel was used. In all examples and except as is indicated in Example 7, where zerogel was employed, all of the examples employed the hydrogel.

The above cogel was pelleted and tested by the microactivity test identified above after steaming at 1450.degree. F. for two hours (M activity) and again another sample after steaming at 1500.degree. F. for two hours (S activity) and a third sample after steaming for two hours at 1550.degree. F. (S+ activity). The results are reported as volume percent conversion. The results obtained were as follows:

______________________________________ M S S+ ______________________________________ Volume % conversion: 43 36.5 46 ______________________________________

The gel was also mixed with acid treated halloysite (see Secor, 2,935,463 and 3,446,727) in the ratio of 90% by weight of the dried gel and 10% by weight of the dry halloysite. The mixture was tested as above with the following results:

______________________________________ M S+ ______________________________________ Volume % conversion: 47 44 ______________________________________

EXAMPLE 2

1,600 grams of the cogel prepared as in Example 1 (calculated on a volatile free basis) was mixed gradually with 18.4 liters of rare earth sulfate solution containing 1.96% of rare earth oxides ReO while the mixture was maintained for about an hour at a pH of 5 by adjustment during the mixing. The composition of the rare earth sulfate expressed as oxides and symbolized as ReO was:

______________________________________ La.sub.2 O.sub.3 = 57% by weight CeO.sub.2 = 16% by weight Nd.sub.2 O.sub.3 = 21% by weight Other rare earth oxides = 7% by weight ______________________________________

100 grams of Reo (volatile free) is equal to 1.896 equivalents of ReO, i.e., 52.7 grams per equivalent.

The ReO was determined by the standard oxalate method. See Roden, "Analytical Chemistry of the Manhatten Project", McGrawHill Co., Chapter 22. In all examples, ReO was similarly determined and had the above equivalent value.

The above mixture was held at the temperature of about 180.degree. to 200.degree. F. for about 2 hours at atmospheric pressure. During the reactions, the pH of the mixture was adjusted to hold a pH in the range of 5.2 to 5.4.

The filter cake was analyzed on a volatile free basis as follows.

______________________________________ SiO.sub.2 = 48.8% by weight Al.sub.2 O.sub.3 = 45.6% by weight ReO = 4.15% by weight NH.sub.3 = 0.3% by weight Na.sub.2 O = 0.06% by weight SO.sub.3 = 0.67% by weight. ______________________________________

The x-ray spectrum obtained as in Example 1, showed lines having the "d" spacings and intensities as in the following Table 1.

TABLE 1 ______________________________________ d I ______________________________________ 6.39 6 6.26 24 4.58 3 3.57 3 3.49 3 3.41 2 3.24 2 3.14 3 3.00 10 2.86 3 2.43 2 2.21 6 ______________________________________

We have designated the above crystal phase as "alpha" and the host gel as "alpha" gel.

The cogel treated as above was slurried in water with 10% of acid treated halloysite and 90% of the cogel all measured on a volatile free basis in Example 1 and subjected to the above test as set forth in Example 1 with the following results:

______________________________________ M S S+ ______________________________________ Volume % conversion 77 62 56 ______________________________________

EXAMPLE 3

The procedure of Example 2 was repeated except the ReO was used in the ratio of 10% by weight of the gel. The exchanged gel had the following composition:

______________________________________ SiO.sub.2 = 44% Al.sub.2 O.sub.3 = 47.6% ReO = 6.81% NH.sub.3 = 0.75% Na.sub.2 O = 0.06% ______________________________________

Examined by x-ray as in Example 1, the pattern showed that the gel contained a crystalline phase substantially different from the product of Example 2. The following Table 2 states the "d" spacings of the reflections.

TABLE 2 ______________________________________ d (Angstroms) I ______________________________________ 8.44 44 4.75 4 4.47 5 4.24 4 4.16 3 3.96 3 3.76 3 3.26 4 3.04 3 2.33 2 ______________________________________

This crystal phase is designated as "beta" and the host gel as "beta" gel.

The exchanged gel when formulated as in Example 1 had the following results:

______________________________________ M = 68.4% S+ = 61.6% ______________________________________

The M activity of the alpha gel is substantially greater than the M activity of the "beta" gel but the hydrothermal stability of the "beta" gel as reflected by the larger S+ activity is substantially superior to the "alpha" gel.

In employing rare earth sulfate for the exchange salt in the hydrolytic treatment of the gel, the improvement in activity obtained by the generation of the beta phase may be depreciated if the temperature or the ratio of the cations to the gel or the time of digestion or both are made excessive. Reference is had to our copending application, Ser. No. 3,879; filed Jan. 16, 1979, and Ser. No. 9,487; filed Feb. 5, 1979 for further details. The acid applications are incorporated herein by this reference.

While we do not wish to be bound by any theory of why the facts are as observed, the data tends to indicate that the hydrolytically treated gel forms, whether it be a crystalline or amorphous, a catalytically active structure which is a metastable form. Continued treatment or excessive temperatures transform the gel and depreciates its activity.

The preferred embodiment of our invention is as stated in Example 3.

Modifications of the temperature, ratios of reactants, pH, time and time of digestion may be adjusted to produce the "beta" gel. Departures from the conditions as set forth in said examples may be made and the deammoniated gel x-rayed as described above. Such variations following the above guides will permit those skilled in the art to produce the "beta" gel of this invention.

It will be understood by those skilled in this art, that the exact values of the "d" spacings of the "beta" crystal phase may vary, for example, plus or minus about 1 or 2% from those of Table due to experimental artifacts and uncertainties in the production of x-ray spectra.

Those skilled in the art will understand from the above disclosure how to determine temperatures, time, cation concentration and ratios to the gel to obtain the desired level of activity. The examples illustrate the procedure and result effective parameters and may act as a guide to those who wish to determine these parameters for their particular conditions and desired result.

The treated gel may be employed with or without a matrix, i.e. alone if desired as for example, as a microsphere obtained by spray drying the slurry of the exchanged product by dispersing the washed filter cake in water and spray drying.

Instead of using the exchanged gel either alone or mixed with a relatively catalytically inactive constituent acting as a matrix such as clay, silica gel or alumina gel or other inorganic oxide such as gel or cogel, the exchanged gels produced according to our invention may be combined with an exchanged zeolite. Such as the ammonium or the rare earth or rare earth and ammonium exchanged zeolites or alkaline with exchanged zeolite either of the faujasite type such as the X or Y zeolite or other crystalline alumino-silicate zeolites such as mordenite, chabazite, erionite, and zeolite A.

The mixture may be in the ratio in the range of about 1% to less about 50% by weight of the zeolite suitably exchanged, if necessary, to a sodium content as in the case of catalysts of the prior art and the above exchanged silica-alumina gel. In the case of an ammonium or a rare earth exchanged Y or exchanged with both NH.sub.4 and ReO, with a Na.sub.2 O ratio of less than 5% by weight on a volatile free basis, we may use a minor proportion of about 1 to less then 50% of zeolite based on the mixture of gel and zeolite. A suitable mixture is about 20% by weight of the zeolite to 80% by weight of the cogel all on a volatile free basis. Such mixtures may suitably be combined with matrix material for zeolites in the prior art.

When using the exchanged "beta" gel with a zeolite, we prefer to use the exchanged gel to be mixed with the rare earth exchanged zeolites of the prior art with an Na.sub.2 O content of less than about 4-5%, for example 3.5% and preferably the so-called A type pseudoboehmite (see U.S. Pat. No. 4,100,108). We prefer to employ the Y zeolite of an SiO.sub.2 /Al.sub.2 O.sub.3 ratio of above 4 for example, 4.5. The percent of the zeolite in the gel zeolite mixture on a volatile free basis may be about 5% to 25% of the mixture.

Instead of mixing the exchanged gel with the exchanged zeolite as above, we may combine the zeolite either in the sodium form or exchanged as above with the gel such as the gel of Example 1. (See our applications Ser. Nos. 769,118, filed Feb. 6, 1977; now U.S. Pat. No. 4,142,995 and 874,755, filed Feb. 3, 1978 now U.S. Pat. No. 4,198,319.) The zeolite may be partially exchanged for example with NH.sub.4 or rare earth or with both for example to reduce the Na.sub.2 O to about 3 to about 6% of the exchanged gel on a volatile free basis. The spray dried zeolite and gel may then be exchanged, preferably with an acid solution of rare earth salts as is described in the above examples.

Our invention includes the use of the hydrothermally treated gel of our invention either alone or combined with a matrix as above, and whether or not combined with a zeolite as described above, in catalytic process other than straight catalytic cracking as described above. Such processes include other hydrocarbon conversion process such as, fore example, hydrocracking, hydroforming and hydrodesulfurizing process. Promoters employed in the prior art in catalysts for such process may be employed with the hydrothermally treated gels of our invention.

Claims

1. An ammoniated silica-alumina gel having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio more than 1 and less than 3, and containing less than 0.3 equivalents of NH.sub.4 cations per mole of Al.sub.2 O.sub.3 in the gel and rare earth cations and a crystalline phase having "d" spacings according to Table 2.

2. An ammoniated silica-alumina gel having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio in the range of in excess of 1 and less than about 2.5 and containing ammonium cation in amount substantially less than 0.3 equivalents per mole of Al.sub.2 O.sub.3 and sodium expressed as Na.sub.2 O of less than about 1% by weight of the exchanged gel on a volatile free basis and a crystalline phase having "d" spacings according to Table 2.

3. An ammoniate silica-alumina gel of SiO.sub.2 /Al.sub.2 O.sub.3 ratio or more than 1 and less than 3 and containing less than 0.3 equivalents of NH.sub.4 cations and from about 0.1 more than 0.4 equivalents of rare earth cations expressed as ReO cations per mole of Al.sub.2 O.sub.3 in the gel and a crystalline phase having "d" spacings according to Table 2.

4. An ammoniated silica-alumina gel having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio in the range of more than 1 and up to about 2 and containing less than about 1.5 equivalents of ammonium cation per mole Al.sub.2 O.sub.3 in the gel and from about 0.1 to more than 0.4 equivalents of ReO per mole of Al.sub.2 O.sub.3 and sodium expressed as Na.sub.2 O of less than about 0.5% by weight of the gel on a volatile free basis and a crystalline phase having "d" spacings according to Table 2.

5. The gel of claims 1, 2, 3, or 4, in which the NH.sub.4 content is less than about 0.15 and the rare earth cations are in the range of about 0.5 to about 5 equivalents per mole of Al.sub.2 O.sub.3 in the gel.